JavaWEB-（二十五）Session

本文最后更新于：December 3, 2021 pm

在WEB开发中，服务器可以为每个用户浏览器创建一个会话对象（session对象），注意：一个浏览器独占一个session对象(默认情况下)。因此，在需要保存用户数据时，服务器程序可以把用户数据写到用户浏览器独占的session中，当用户使用浏览器访问其它程序时，其它程序可以从用户的session中取出该用户的数据，为用户服务。

目录

1.Session概述

Session用于记录用户的状态。Session指的是在一段时间内，单个客户端与web服务器的一连串相关的交互过程。在一个Session中，用户可能会多次请求访问同一个资源，也有可能请求访问各种不同的服务器资源。

1.1 Session原理

  • 服务器会为每一次会话分配一个Session对象。
  • 同一个浏览器发起的多次请求，属于同一次会话（Session）。
  • 首次使用到Session时，服务器会自动创建Session，并创建Cookie存储SessionId发送回客户端。

2.Session使用

Session作用域：拥有存储数据的空间，作业范围是一次会话有效。

  • 一次会话是使用同一浏览器发送的多次请求。一旦浏览器关闭，则会话结束。
  • 可以将数据存入Session中，在一次会话的任意位置进行获取。
  • 可传递任何数据（基本数据类型、对象、集合、数组）。

2.1 获取Session

HttpSession session = request.getSession();

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/ss")
public class SessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession httpSession = req.getSession();
        System.out.println(httpSession.getId()); //唯一标记
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

可以尝试多次刷新页面和把浏览器关闭完后再次访问，在控制台可以发现其Session的Id是不同的。

2.2 Session保存数据

setAttribute(属性名，Object); 保存数据到Session中。

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session.setAttribute("key","value"); //以键值对形式存储在Session作用域中

2.3 Session获取数据

getAttribute(属性名); 获取Session中的数据。

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session.getAttribute("key"); //通过String类型的key访问Object类型的value，所以取时需要强转

2.4 Session移除数据

removeAttribute(属性名); 从Session中删除数据。

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session.removeAttribute("key"); //通过键移除Session作用域中的值

2.5 示例

设置Session：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/ss")
public class SessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession httpSession = req.getSession();
        httpSession.setAttribute("username","loongloong");
        System.out.println(httpSession.getId());
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

获取Session：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/gs")
public class getSession extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        String s = (String) session.getAttribute("username");
        System.out.println("拿到的Session "+ s);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

移除Session：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/rs")
public class removeSession extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        session.removeAttribute("username");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

浏览器访问顺序：ss -> gs -> rs -> gs

结果：

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5EA82F3C98E15F679A51A0CDA3B206D9
拿到的Session loongloong
拿到的Session null

3.Session与Request应用区别

  • request是一次请求有效，请求改变，request改变。（可以用重定向来验证，因为重定向属于至少两次请求。）
  • session是一次会话有效，浏览器改变，session改变。

3.1 示例

创建：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/ss")
public class SessionServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession httpSession = req.getSession();
        
        httpSession.setAttribute("username","loongloong");
        req.setAttribute("password","123456789");
        resp.sendRedirect("/Cook_war_exploded/gs"); //重定向是两次请求，用来区别

        System.out.println(httpSession.getId());
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

获取：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/gs")
public class getSession extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        String s = (String) session.getAttribute("username");
        String sp = (String) req.getAttribute("password");
        System.out.println("拿到的Session "+ s);
        System.out.println("拿到的request "+ sp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

执行顺序：ss -> gs

结果：

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117F44C3098BED68DF1B14FDC5174469
拿到的Session loongloong
拿到的request null

表明，request的作用域只能在一次请求以内有效。通过重定向（两次请求）就无法传递数据。

4.Session的生命周期

开始是第一次使用到Session的请求而产生。而结束有多种：

    1. 浏览器关闭，则失效
    1. Session超时，则失效。session.setMaiInactiveInterval(seconds)；设置最大有效时间，单位为秒。
    1. 手动销毁，则失效。 session.invalidate(); 用于登录退出、注销。

4.1 session.setMaiInactiveInterval(seconds)

设置：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/ls1")
public class life1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        session.setMaxInactiveInterval(10);
        System.out.println(session.getId());
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

获取：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/ls2")


public class life2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        System.out.println(session.getId());
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

执行顺序：ls1 -> ls2（10s内）-> ls2（10s后）

结果：

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9522290829E9266AC4021BF3D55B37EA
9522290829E9266AC4021BF3D55B37EA
772A0C698222A48A0A8BFF6516FCEB46

4.2 session.invalidate()

设置：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/ls1")
public class life1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        System.out.println(session.getId());
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

获取：

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package com.tothefor.sessionP;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(value = "/ls2")


public class life2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        System.out.println(session.getId());
        session.invalidate();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

执行顺序：ls1 -> ls2 -> ls1

结果

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39F75884C151F046C8C980B95869FC89
39F75884C151F046C8C980B95869FC89
39B8B8AB16E46106012957083BBE5653
JavaWEB
JavaWEB

本文作者: 墨水记忆
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